The vehicle electronic key makes it possible to unlock a door and start an engine by being verified by a wireless communication with a vehicle (refer to Patent Literature 1). Since such a vehicle electronic key is driven by a power supply such as a battery, the vehicle electronic key cannot be used when the battery runs out, but in consideration of this point, a mechanical key is contained inside of the vehicle electronic key.
The mechanical key is different in frequency of use depending on users. In other words, there are users who do not use the mechanical key much and mainly use the wireless communication, and users who do not use the wireless communication much and mainly use the mechanical key. An optimum design of the key is different depending on the two types of the users. For example, the users who mainly use the wireless communication desire a design that reliably accommodates the mechanical key. On the other hand, the users who mainly use the mechanical key emphasize ease of taking out the mechanical key.
However, it is difficult to realize the design of the vehicle electronic key that satisfies both of those requirements, and it is sometimes necessary to separately prepare each key. For that reason, two or more keys different in design exist to one vehicle, which may increase the waste of cost.